You need to find the derivative.Originally Posted byHallah_az

Thus, you have

Its derivative is the power rule, thus,

At, point we have, .

Now we use the point-intercept formula. Which says that if a line passes through point and has slope then, its equation is,

. Thus, in this case we have the point, which is . Now we need the slope. That is the derivative evaluated at that point which is the equation is,

Thus,

Thus,